Thermal Radiometer Signal Processing using ...

Thermal Radiometer Signal Processing using Radiation Hard CMOS Application Specific Integrated Circuits for use in Harsh Planetary Environments G. Quilligan, J. DuMonthier, S. Aslam, B. Lakew, I. Kleyner, and R. Katz

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Topics • Introduction • Radiometer Focal Plane Array • Multi-Channel Digitizer ASIC • Performance in a high dose radiation environment • Summary and concluding remarks

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Introduction • Space based thermal radiometers are used to detect infra-red radiation emitted by planetary bodies • They enable remote measurement of •  day/night surface temperatures of an icy moon such as Europa •  endogenic heat flux •  hotspot and geothermal anomalies

• The thermal radiometer consists of a ‘telescope’ with motor driven optics and a focal plane array (FPA) to detect the radiation gathered by the optics • The FPA contains readout electronics which must be able to operate in a harsh environment such as the Jovian orbital system EPSC 2015

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Thermal Radiometers • Thermal radiometers utilize thermopiles or bolometers –  Thermopiles output a voltage proportional to incident thermal radiation •  Linear voltage response •  No special biasing requirements •  Thermopile temperature must be monitored (e.g. using a thermistor or diode)

–  Bolometers output a voltage proportional to incident thermal radiation and a user supplied bias current •  Linear resistance response •  Require per pixel bias currents •  Highest sensitivity and lowest noise from cooled bolometers

• Thermal radiometer sensors are built as focal plane arrays –  –  –  – 

Pixels are organized as linear or area arrays Pixels are read-out as N x 1 lines or in N x M arrays Read-out circuits are in close proximity to the pixels Read-out requires ‘parallel’ analog signal processing •  Amplification •  Filtering •  Digitization

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Requirements • Thermal radiometer electrical requirements –  –  –  – 

Signal processing of hundreds or even thousands of pixels Amplification of low voltages by at least 103 Low 1/f and thermal noise Digitization to > 12 bits

• Space Environment imposes additional specifications –  Operation in high total ionizing dose (TID) environments •  NMOS transistor drain-source leakage •  Varying PMOS/NMOS threshold voltages cause large offsets

–  Operation in high energy particle environments •  Single event latchup (SEL) •  Single event upset (SEU) •  Single event transient (SET)

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Jovian Radiation Belts Similar to Van Allen belts, but millions of times more intense

http://www.nasm.si.edu/etp/jupiter/jupimg/JUP_magfield.gif EPSC 2015

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Jovian Radiation Model and Environment • Radiation is a unique challenge for instrument electronics due to significant time spent in harsh Jovian radiation belts –  Unprecedented for long duration NASA missions

• The instrument is subjected to four major radiation sources: –  Solar energetic particles (protons, electrons, and heavy ions) during the interplanetary cruise –  Galactic cosmic rays (protons and heavy ions) during the interplanetary cruise –  Trapped particles (electrons, protons, and heavy ions) in the Jovian magnetosphere during the Jupiter tour and the orbits at Europa –  Particles (neutrons and gammas) from the onboard nuclear power source, MMRTG

• High-energy trapped electrons and protons at Jupiter are dominant contributors to TID and DDD effects

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Radiation Requirements Aluminum Dose Depth Curve

From Jupiter Europa Orbiter Mission Study 2008: Final Report EPSC 2015

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Particle Fluences 1.E+17

Europa (Electrons)

Par$cle  Fluence  (cm-­‐2)  

1.E+16

Europa (Jovian Tour)

1.E+15

Protons (Europa)

1.E+14

Protons (Jovian Tour)

1.E+13 1.E+12 1.E+11 1.E+10 1.E+09 1.E+08 0.1  

1  

10  

100  

Particle Energy (MeV)

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FPA Application Schematic 320 Pixel Thermopile Line Array

Digitizer Bank

40 Pixels

MCD ASIC 1

40 Pixels

MCD ASIC 2

Data/ Control

Planet/Moon/ Asteroid

E=hf

320 pixels + 1 triplet

Thermistor

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40 Pixels

MCD ASIC 3

40 Pixels

MCD ASIC 8

Bias current

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64 Pixel Thermopile Example

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Focal Plane Array Hybrid Circuit

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Key ASIC Specifications • Number of channels: 40 –  8 ASICs interface to a 320 pixel array

• Radiation hardness: 3Mrad TID and no SEL –  Jovian environment near Europa

• Process technology: 180nm Towerjazz CMOS (CA18HD) –  1.8V CMOS has lower sensitivity to threshold variation vs. TID –  Baseline non-hardened process is radiation tolerant

• ADC resolution: 16 bits • Radiometer Resolution / Linearity: 2K / 0.2% • Noise: 50Mrad –  No SEL > 174 MeV-cm2/mg –  TA